Wireless power transfer (WPT) systems can transfer power through free space from transmitting units to receiving units. WPT systems may be used to charge electric vehicles, as well as charging mobile devices, medical devices, etc. Some wireless power transfer systems can utilize inductive power transfer where power is transferred through magnetic coupling between two magnetic field coupling units (i.e., a primary coupler and a secondary coupler). These coupling units generally include single or multiple windings of electric current carrying material, typically Litz wire, which may be configured to create different magnetic flux distributions.
The application of wireless power transfer for electric vehicle charging may generate magnetic field exposure to the surrounding area of the vehicle affecting overall system efficiency. One of the key factors in determining the overall system efficiency is the quality of the magnetic field coupling between the primary and secondary couplers. System efficiency can be improved by improving the magnetic field coupling between the primary and secondary coils. The amount of human exposure to magnetic fields generated by the inductive wireless power transfer is dependent on the field strength. The fields generated by the inductive WPT system are reactive near fields and typically field strength decays with the inverse cube of distance from the coupler. Even though fields from the inductive WPT system decay quickly with distance, it may be desirable to minimize the field strength in human accessible locations.